/*

 * wrgif.c

 *

 * Copyright (C) 1991-1994, Thomas G. Lane.

 * This file is part of the Independent JPEG Group's software.

 * For conditions of distribution and use, see the accompanying README file.

 *

 **************************************************************************

 * WARNING: You will need an LZW patent license from Unisys in order to   *

 * use this file legally in any commercial or shareware application.      *

 **************************************************************************

 *

 * This file contains routines to write output images in GIF format.

 *

 * These routines may need modification for non-Unix environments or

 * specialized applications.  As they stand, they assume output to

 * an ordinary stdio stream.

 */



/*

 * This code is loosely based on ppmtogif from the PBMPLUS distribution

 * of Feb. 1991.  That file contains the following copyright notice:

 *    Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>.

 *    Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al.

 *    Copyright (C) 1989 by Jef Poskanzer.

 *    Permission to use, copy, modify, and distribute this software and its

 *    documentation for any purpose and without fee is hereby granted, provided

 *    that the above copyright notice appear in all copies and that both that

 *    copyright notice and this permission notice appear in supporting

 *    documentation.  This software is provided "as is" without express or

 *    implied warranty.

 *

 * We are also required to state that

 *    "The Graphics Interchange Format(c) is the Copyright property of

 *    CompuServe Incorporated. GIF(sm) is a Service Mark property of

 *    CompuServe Incorporated."

 */



#include "cdjpeg.h"		/* Common decls for cjpeg/djpeg applications */



#ifdef GIF_SUPPORTED





#define	MAX_LZW_BITS	12	/* maximum LZW code size (4096 symbols) */



typedef INT16 code_int;		/* must hold -1 .. 2**MAX_LZW_BITS */



#define LZW_TABLE_SIZE	((code_int) 1 << MAX_LZW_BITS)



#define HSIZE		5003	/* hash table size for 80% occupancy */



typedef int hash_int;		/* must hold -2*HSIZE..2*HSIZE */



#define MAXCODE(n_bits)	(((code_int) 1 << (n_bits)) - 1)





/*

 * The LZW hash table consists of two parallel arrays:

 *   hash_code[i]	code of symbol in slot i, or 0 if empty slot

 *   hash_value[i]	symbol's value; undefined if empty slot

 * where slot values (i) range from 0 to HSIZE-1.  The symbol value is

 * its prefix symbol's code concatenated with its suffix character.

 *

 * Algorithm:  use open addressing double hashing (no chaining) on the

 * prefix code / suffix character combination.  We do a variant of Knuth's

 * algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime

 * secondary probe.

 *

 * The hash_value[] table is allocated from FAR heap space since it would

 * use up rather a lot of the near data space in a PC.

 */



typedef INT32 hash_entry;	/* must hold (code_int<<8) | byte */



#define HASH_ENTRY(prefix,suffix)  ((((hash_entry) (prefix)) << 8) | (suffix))





/* Private version of data destination object */



typedef struct {

  struct djpeg_dest_struct pub;	/* public fields */



  j_decompress_ptr cinfo;	/* back link saves passing separate parm */



  /* State for packing variable-width codes into a bitstream */

  int n_bits;			/* current number of bits/code */

  code_int maxcode;		/* maximum code, given n_bits */

  int init_bits;		/* initial n_bits ... restored after clear */

  INT32 cur_accum;		/* holds bits not yet output */

  int cur_bits;			/* # of bits in cur_accum */



  /* LZW string construction */

  code_int waiting_code;	/* symbol not yet output; may be extendable */

  boolean first_byte;		/* if TRUE, waiting_code is not valid */



  /* State for LZW code assignment */

  code_int ClearCode;		/* clear code (doesn't change) */

  code_int EOFCode;		/* EOF code (ditto) */

  code_int free_code;		/* first not-yet-used symbol code */



  /* LZW hash table */

  code_int *hash_code;		/* => hash table of symbol codes */

  hash_entry FAR *hash_value;	/* => hash table of symbol values */



  /* GIF data packet construction buffer */

  int bytesinpkt;		/* # of bytes in current packet */

  char packetbuf[256];		/* workspace for accumulating packet */



} gif_dest_struct;



typedef gif_dest_struct * gif_dest_ptr;





/*

 * Routines to package compressed data bytes into GIF data blocks.

 * A data block consists of a count byte (1..255) and that many data bytes.

 */



LOCAL void

flush_packet (gif_dest_ptr dinfo)

/* flush any accumulated data */

{

  if (dinfo->bytesinpkt > 0) {	/* never write zero-length packet */

    dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++;

    if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt)

	!= (size_t) dinfo->bytesinpkt)

      ERREXIT(dinfo->cinfo, JERR_FILE_WRITE);

    dinfo->bytesinpkt = 0;

  }

}





/* Add a character to current packet; flush to disk if necessary */

#define CHAR_OUT(dinfo,c)  \

	{ (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c);  \

	    if ((dinfo)->bytesinpkt >= 255)  \

	      flush_packet(dinfo);  \

	}





/* Routine to convert variable-width codes into a byte stream */



LOCAL void

output (gif_dest_ptr dinfo, code_int code)

/* Emit a code of n_bits bits */

/* Uses cur_accum and cur_bits to reblock into 8-bit bytes */

{

  dinfo->cur_accum |= ((INT32) code) << dinfo->cur_bits;

  dinfo->cur_bits += dinfo->n_bits;



  while (dinfo->cur_bits >= 8) {

    CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);

    dinfo->cur_accum >>= 8;

    dinfo->cur_bits -= 8;

  }



  /*

   * If the next entry is going to be too big for the code size,

   * then increase it, if possible.  We do this here to ensure

   * that it's done in sync with the decoder's codesize increases.

   */

  if (dinfo->free_code > dinfo->maxcode) {

    dinfo->n_bits++;

    if (dinfo->n_bits == MAX_LZW_BITS)

      dinfo->maxcode = LZW_TABLE_SIZE; /* free_code will never exceed this */

    else

      dinfo->maxcode = MAXCODE(dinfo->n_bits);

  }

}





/* The LZW algorithm proper */





LOCAL void

clear_hash (gif_dest_ptr dinfo)

/* Fill the hash table with empty entries */

{

  /* It's sufficient to zero hash_code[] */

  MEMZERO(dinfo->hash_code, HSIZE * SIZEOF(code_int));

}





LOCAL void

clear_block (gif_dest_ptr dinfo)

/* Reset compressor and issue a Clear code */

{

  clear_hash(dinfo);			/* delete all the symbols */

  dinfo->free_code = dinfo->ClearCode + 2;

  output(dinfo, dinfo->ClearCode);	/* inform decoder */

  dinfo->n_bits = dinfo->init_bits;	/* reset code size */

  dinfo->maxcode = MAXCODE(dinfo->n_bits);

}





LOCAL void

compress_init (gif_dest_ptr dinfo, int i_bits)

/* Initialize LZW compressor */

{

  /* init all the state variables */

  dinfo->n_bits = dinfo->init_bits = i_bits;

  dinfo->maxcode = MAXCODE(dinfo->n_bits);

  dinfo->ClearCode = ((code_int) 1 << (i_bits - 1));

  dinfo->EOFCode = dinfo->ClearCode + 1;

  dinfo->free_code = dinfo->ClearCode + 2;

  dinfo->first_byte = TRUE;	/* no waiting symbol yet */

  /* init output buffering vars */

  dinfo->bytesinpkt = 0;

  dinfo->cur_accum = 0;

  dinfo->cur_bits = 0;

  /* clear hash table */

  clear_hash(dinfo);

  /* GIF specifies an initial Clear code */

  output(dinfo, dinfo->ClearCode);

}





LOCAL void

compress_byte (gif_dest_ptr dinfo, int c)

/* Accept and compress one 8-bit byte */

{

  register hash_int i;

  register hash_int disp;

  register hash_entry probe_value;



  if (dinfo->first_byte) {	/* need to initialize waiting_code */

    dinfo->waiting_code = c;

    dinfo->first_byte = FALSE;

    return;

  }



  /* Probe hash table to see if a symbol exists for

   * waiting_code followed by c.

   * If so, replace waiting_code by that symbol and return.

   */

  i = ((hash_int) c << (MAX_LZW_BITS-8)) + dinfo->waiting_code;

  /* i is less than twice 2**MAX_LZW_BITS, therefore less than twice HSIZE */

  if (i >= HSIZE)

    i -= HSIZE;



  probe_value = HASH_ENTRY(dinfo->waiting_code, c);

  

  if (dinfo->hash_code[i] != 0) { /* is first probed slot empty? */

    if (dinfo->hash_value[i] == probe_value) {

      dinfo->waiting_code = dinfo->hash_code[i];

      return;

    }

    if (i == 0)			/* secondary hash (after G. Knott) */

      disp = 1;

    else

      disp = HSIZE - i;

    for (;;) {

      i -= disp;

      if (i < 0)

	i += HSIZE;

      if (dinfo->hash_code[i] == 0)

	break;			/* hit empty slot */

      if (dinfo->hash_value[i] == probe_value) {

	dinfo->waiting_code = dinfo->hash_code[i];

	return;

      }

    }

  }



  /* here when hashtable[i] is an empty slot; desired symbol not in table */

  output(dinfo, dinfo->waiting_code);

  if (dinfo->free_code < LZW_TABLE_SIZE) {

    dinfo->hash_code[i] = dinfo->free_code++; /* add symbol to hashtable */

    dinfo->hash_value[i] = probe_value;

  } else

    clear_block(dinfo);

  dinfo->waiting_code = c;

}





LOCAL void

compress_term (gif_dest_ptr dinfo)

/* Clean up at end */

{

  /* Flush out the buffered code */

  if (! dinfo->first_byte)

    output(dinfo, dinfo->waiting_code);

  /* Send an EOF code */

  output(dinfo, dinfo->EOFCode);

  /* Flush the bit-packing buffer */

  if (dinfo->cur_bits > 0) {

    CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);

  }

  /* Flush the packet buffer */

  flush_packet(dinfo);

}





/* GIF header construction */





LOCAL void

put_word (gif_dest_ptr dinfo, unsigned int w)

/* Emit a 16-bit word, LSB first */

{

  putc(w & 0xFF, dinfo->pub.output_file);

  putc((w >> 8) & 0xFF, dinfo->pub.output_file);

}





LOCAL void

put_3bytes (gif_dest_ptr dinfo, int val)

/* Emit 3 copies of same byte value --- handy subr for colormap construction */

{

  putc(val, dinfo->pub.output_file);

  putc(val, dinfo->pub.output_file);

  putc(val, dinfo->pub.output_file);

}





LOCAL void

emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap)

/* Output the GIF file header, including color map */

/* If colormap==NULL, synthesize a gray-scale colormap */

{

  int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte;

  int cshift = dinfo->cinfo->data_precision - 8;

  int i;



  if (num_colors > 256)

    ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors);

  /* Compute bits/pixel and related values */

  BitsPerPixel = 1;

  while (num_colors > (1 << BitsPerPixel))

    BitsPerPixel++;

  ColorMapSize = 1 << BitsPerPixel;

  if (BitsPerPixel <= 1)

    InitCodeSize = 2;

  else

    InitCodeSize = BitsPerPixel;

  /*

   * Write the GIF header.

   * Note that we generate a plain GIF87 header for maximum compatibility.

   */

  putc('G', dinfo->pub.output_file);

  putc('I', dinfo->pub.output_file);

  putc('F', dinfo->pub.output_file);

  putc('8', dinfo->pub.output_file);

  putc('7', dinfo->pub.output_file);

  putc('a', dinfo->pub.output_file);

  /* Write the Logical Screen Descriptor */

  put_word(dinfo, (unsigned int) dinfo->cinfo->output_width);

  put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);

  FlagByte = 0x80;		/* Yes, there is a global color table */

  FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */

  FlagByte |= (BitsPerPixel-1);	/* size of global color table */

  putc(FlagByte, dinfo->pub.output_file);

  putc(0, dinfo->pub.output_file); /* Background color index */

  putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */

  /* Write the Global Color Map */

  /* If the color map is more than 8 bits precision, */

  /* we reduce it to 8 bits by shifting */

  for (i=0; i < ColorMapSize; i++) {

    if (i < num_colors) {

      if (colormap != NULL) {

	if (dinfo->cinfo->out_color_space == JCS_RGB) {

	  /* Normal case: RGB color map */

	  putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file);

	  putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file);

	  putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file);

	} else {

	  /* Grayscale "color map": possible if quantizing grayscale image */

	  put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift);

	}

      } else {

	/* Create a gray-scale map of num_colors values, range 0..255 */

	put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1));

      }

    } else {

      /* fill out the map to a power of 2 */

      put_3bytes(dinfo, 0);

    }

  }

  /* Write image separator and Image Descriptor */

  putc(',', dinfo->pub.output_file); /* separator */

  put_word(dinfo, 0);		/* left/top offset */

  put_word(dinfo, 0);

  put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */

  put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);

  /* flag byte: not interlaced, no local color map */

  putc(0x00, dinfo->pub.output_file);

  /* Write Initial Code Size byte */

  putc(InitCodeSize, dinfo->pub.output_file);



  /* Initialize for LZW compression of image data */

  compress_init(dinfo, InitCodeSize+1);

}





/*

 * Startup: write the file header.

 */



METHODDEF void

start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)

{

  gif_dest_ptr dest = (gif_dest_ptr) dinfo;



  if (cinfo->quantize_colors)

    emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap);

  else

    emit_header(dest, 256, (JSAMPARRAY) NULL);

}





/*

 * Write some pixel data.

 * In this module rows_supplied will always be 1.

 */



METHODDEF void

put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo,

		JDIMENSION rows_supplied)

{

  gif_dest_ptr dest = (gif_dest_ptr) dinfo;

  register JSAMPROW ptr;

  register JDIMENSION col;



  ptr = dest->pub.buffer[0];

  for (col = cinfo->output_width; col > 0; col--) {

    compress_byte(dest, GETJSAMPLE(*ptr++));

  }

}





/*

 * Finish up at the end of the file.

 */



METHODDEF void

finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)

{

  gif_dest_ptr dest = (gif_dest_ptr) dinfo;



  /* Flush LZW mechanism */

  compress_term(dest);

  /* Write a zero-length data block to end the series */

  putc(0, dest->pub.output_file);

  /* Write the GIF terminator mark */

  putc(';', dest->pub.output_file);

  /* Make sure we wrote the output file OK */

  fflush(dest->pub.output_file);

  if (ferror(dest->pub.output_file))

    ERREXIT(cinfo, JERR_FILE_WRITE);

}





/*

 * The module selection routine for GIF format output.

 */



GLOBAL djpeg_dest_ptr

jinit_write_gif (j_decompress_ptr cinfo)

{

  gif_dest_ptr dest;



  /* Create module interface object, fill in method pointers */

  dest = (gif_dest_ptr)

      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				  SIZEOF(gif_dest_struct));

  dest->cinfo = cinfo;		/* make back link for subroutines */

  dest->pub.start_output = start_output_gif;

  dest->pub.put_pixel_rows = put_pixel_rows;

  dest->pub.finish_output = finish_output_gif;



  if (cinfo->out_color_space != JCS_GRAYSCALE &&

      cinfo->out_color_space != JCS_RGB)

    ERREXIT(cinfo, JERR_GIF_COLORSPACE);



  /* Force quantization if color or if > 8 bits input */

  if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) {

    /* Force quantization to at most 256 colors */

    cinfo->quantize_colors = TRUE;

    if (cinfo->desired_number_of_colors > 256)

      cinfo->desired_number_of_colors = 256;

  }



  /* Calculate output image dimensions so we can allocate space */

  jpeg_calc_output_dimensions(cinfo);



  if (cinfo->output_components != 1) /* safety check: just one component? */

    ERREXIT(cinfo, JERR_GIF_BUG);



  /* Create decompressor output buffer. */

  dest->pub.buffer = (*cinfo->mem->alloc_sarray)

    ((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION) 1);

  dest->pub.buffer_height = 1;



  /* Allocate space for hash table */

  dest->hash_code = (code_int *)

    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				HSIZE * SIZEOF(code_int));

  dest->hash_value = (hash_entry FAR *)

    (*cinfo->mem->alloc_large) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				HSIZE * SIZEOF(hash_entry));



  return (djpeg_dest_ptr) dest;

}



#endif /* GIF_SUPPORTED */

